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Revenue from Contracts with Customers - Impact to Financial Statements Affected by Adoption of Topic 606 (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |
Equipment held for sale | $ 789 |  |  |  | $ 34,172 |  |  |  | $ 789 | $ 34,172 |
Spare parts inventory | 48,874 |  |  |  | 16,379 |  |  |  | 48,874 | 16,379 |
Revenue: |  |  |  |  |  |  |  |  |  |  |
Spare parts and equipment sales |  |  |  |  |  |  |  |  | 71,141 | 51,423 | $ 17,783
Gain on sale of leased equipment |  |  |  |  |  |  |  |  | 6,944 | 4,929 | 3,482
Expenses: |  |  |  |  |  |  |  |  |  |  |
Cost of spare parts and equipment sales |  |  |  |  |  |  |  |  | 61,025 | 40,848 | 13,293
Net income |  |  |  |  |  |  |  |  | 43,231 | 62,158 | 14,069
Net income attributable to common shareholders | 17,274 | $ 8,834 | $ 7,528 | $ 6,261 | $ 41,864 | $ 4,939 | $ 5,657 | $ 7,839 | 39,898 | $ 60,299 | $ 13,780
Increase in cash flows from operating activities |  |  |  |  |  |  |  |  | 16,900 |  |
Decrease in proceeds from sale of equipment |  |  |  |  |  |  |  |  | 16,900 |  |
ASU 2014-09 | Balance without adoption of ASC Topic 606 |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |
Equipment held for sale | 23,733 |  |  |  |  |  |  |  | 23,733 |  |
Spare parts inventory | 25,930 |  |  |  |  |  |  |  | 25,930 |  |
Revenue: |  |  |  |  |  |  |  |  |  |  |
Spare parts and equipment sales |  |  |  |  |  |  |  |  | 54,749 |  |
Gain on sale of leased equipment |  |  |  |  |  |  |  |  | 7,644 |  |
Expenses: |  |  |  |  |  |  |  |  |  |  |
Cost of spare parts and equipment sales |  |  |  |  |  |  |  |  | 45,333 |  |
Net income |  |  |  |  |  |  |  |  | 43,231 |  |
Net income attributable to common shareholders |  |  |  |  |  |  |  |  | 39,898 |  |
ASU 2014-09 | Impact of adoption |  |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |  |
Equipment held for sale | (22,944) |  |  |  |  |  |  |  | (22,944) |  |
Spare parts inventory | $ 22,944 |  |  |  |  |  |  |  | 22,944 |  |
Revenue: |  |  |  |  |  |  |  |  |  |  |
Spare parts and equipment sales |  |  |  |  |  |  |  |  | 16,392 |  |
Gain on sale of leased equipment |  |  |  |  |  |  |  |  | (700) |  |
Expenses: |  |  |  |  |  |  |  |  |  |  |
Cost of spare parts and equipment sales |  |  |  |  |  |  |  |  | $ 15,692 |  |

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